The debate begins at 9 p.m. and is being broadcast from Milwaukee on WISN Channel 12.
Walker and Barrett held their first debate on Friday night. Barrett was aggressive in his attacks on Walker in that contest, but Walker stood his ground in defending his record as governor over the past 18 months.
Turnout in Tuesday's election is predicted to be as high as 65 percent, which is nearing levels normally seen in presidential contests.
Walker has raised about $31 million since taking office, including about $20 million this year, in an effort to fend off the recall. Barrett, who got into the race on March 30, has raised about $4.2 million.